Commit e442a0ecc23d315f99f62684c6240e7c1cb6e9ce | zig

author	Ryan Liptak <squeek502@hotmail.com> 2025-12-20 20:18:07-08:00
committer	Andrew Kelley <andrew@ziglang.org> 2025-12-23 22:15:11-08:00
log	e442a0ecc23d315f99f62684c6240e7c1cb6e9ce
tree	2e034d8953310f01d219f7f65e6cc2db3eea73f8
parent	ad08117e9daf5d2a34be1ca71a23366f39079990

Dir.readFile/readFileAlloc: take advantage of `.allow_directory = false` on Windows

Since we know the read will fail for directories, we can take advantage
of Windows being able to fail with IsDir during open to avoid needing to
wait until the read to find out about the directory-ness of the file.

1 files changed, 10 insertions(+), 2 deletions(-)

lib
- std
  - Io
    Dir.zig

lib/std/Io/Dir.zig+10-2

 @@ -633,7 +633,11 @@ pub const ReadFileError = File.OpenError || File.Reader.Error;
 /// * On WASI, `file_path` should be encoded as valid UTF-8.
 /// * On other platforms, `file_path` is an opaque sequence of bytes with no particular encoding.
 pub fn readFile(dir: Dir, io: Io, file_path: []const u8, buffer: []u8) ReadFileError![]u8 {
-    var file = try dir.openFile(io, file_path, .{});
+    var file = try dir.openFile(io, file_path, .{
+        // We can take advantage of this on Windows since it doesn't involve any extra syscalls,
+        // so we can get error.IsDir during open rather than during the read.
+        .allow_directory = if (native_os == .windows) false else true,
+    });
     defer file.close(io);
     var reader = file.reader(io, &.{});
 @@ -1217,7 +1221,11 @@ pub fn readFileAllocOptions(
     comptime alignment: std.mem.Alignment,
     comptime sentinel: ?u8,
 ) ReadFileAllocError!(if (sentinel) |s| [:s]align(alignment.toByteUnits()) u8 else []align(alignment.toByteUnits()) u8) {
-    var file = try dir.openFile(io, sub_path, .{});
+    var file = try dir.openFile(io, sub_path, .{
+        // We can take advantage of this on Windows since it doesn't involve any extra syscalls,
+        // so we can get error.IsDir during open rather than during the read.
+        .allow_directory = if (native_os == .windows) false else true,
+    });
     defer file.close(io);
     var file_reader = file.reader(io, &.{});
     return file_reader.interface.allocRemainingAlignedSentinel(gpa, limit, alignment, sentinel) catch |err| switch (err) {